The present invention relates to the generation of ions, and more particularly to the generation of ions with increased output currents over a prolonged period.
Ions can be generated in a wide variety of ways. Common techniques include the use of air gap breakdown, corona discharges, and spark discharges. Other techniques employ triboelectricity, radiation (alpha, beta, and gamma as well as x-rays and ultraviolet light), and microwave breakdown.
When utilized for the formation of latent electrostatic image, all of the above techniques suffer certain limitations in ion output currents and charge image integrity. A further approach which offers significant improvement in this regard is described in U.S. Pat. No. 4,155,093 and the improvement patent U.S. Pat. No. 4,160,257. These patents disclose method and apparatus for ion generating involving what the inventors term "glow discharge". This is accomplished through the application of a high voltage time-varying potential between two electrodes separated by a solid dielectric member. As disclosed in U.S. Pat. No. 4,155,093, the varying potential causes the formation of a pool of positive and negative ions in an air region adjacent an edge surface of one of the electrodes, which ions may be extracted to form a latent electrostatic image. U.S. Pat. No. 4,160,257 discloses the use of an additional electrode to screen the extraction of ions, providing an electrostatic lensing action and preventing accidental image erasure.
In the preferred embodiment of the ion generation apparatus discussed above, the solid dielectic member comprises a sheet of mica. An advantageous method for fabricating such devices is disclosed in U.S. Pat. No. 4,381,327. A mica sheet is bonded to metal foils using pressure sensitive adhesive, and the metal foils etched in a desired electrode pattern. This fabrication provides excellent ion output currents and reasonable service life. Such devices, however, are commonly exposed to atmospheric environmental substances and byproducts of the ion generation process, which contributes to corrosion thereof. This apparatus also suffers the tendency to accumulate contaminants at the ion generation sites. Such contaminant buildup and corrosion seriously reduce the service life of these devices.
Accordingly, it is a primary object of the invention to provide improved ion generation using a glow discharge ion generator. A related object is to achieve a method which is compatible with a glow discharge ion generator incorporating a mica dielectric.
Another object of the invention is to attain enhanced ion current outputs. A related object is the formation of latent electrostatic images at higher speeds and with lower drive voltage requirements.
A further object of the invention is the achievement of prolonged service life in ion generators of the glow discharge type. A related object is the reduction of contaminant buildup during ion generation. Yet another related object is diminished corrosion of such devices.